Need water tank - Holmes Products HM1851-U 4 Gallon Humidifier

Here are the steps to fill the water tank of the Air Innovation humidifier model A1-KS30U-06C:

1. Turn off the humidifier and unplug it from the power source.
2. Remove the water tank from the base of the humidifier by lifting it straight up.
3. Flip the water tank over and unscrew the cap from the bottom of the tank in a counterclockwise direction.
4. Fill the tank with clean, cool water. Do not overfill the tank; leave some space at the top to prevent spills.
5. Screw the cap back onto the bottom of the tank in a clockwise direction until it is snug.
6. Turn the water tank right side up and carefully place it back onto the base of the humidifier. Make sure it is seated properly and securely.
7. Plug the humidifier back in and turn it on.

Once the tank is filled with water, the humidifier should operate normally and begin adding moisture to the air. It is recommended to clean the water tank periodically to prevent buildup of mineral deposits and bacteria.

try to check the insulation of your drain pan because of your water came from your unit is cold that create moist on the tank when hit by hot air from sorrounding air apply insulation on the tank.

I think you can find another one on amazon, take a look: Amazon com v745a tank. I hope this was helpful. Have a nice day

FILLING THE WATER TANKS
1. Before filling the water tanks, push the POWER switch to the “OFF” position and
unplug unit. Refer to cleaning instructions.
2. Remove water tanks from base, turn each tank upside down and remove tank cap
by turning counterclockwise. Fill tank with clean cold tap water.
Replace the tank cap by turning clockwise. Tighten firmly.
3. Carefully pick up tank, since it will be heavy when full, and slippery if wet.
4. Place water tanks on base. Make sure tanks are properly placed, otherwise, the
humidifier will not work correctly.

The instruction manual suggests using the water vinegar solution.
The following is from the manual.
1. Turn the humidifier ‘OFF’ and unplug the unit.
2. Lift the main housing and remove the water dispersion tray and the PermaWick™ Filters. The motor is attached to the main housing. Do not place the motor near water. Do not use a wet towel on the motor or motor housing as electrical shock may occur.
3. The PermaWick™ Filter should be cleaned in a vinegar and water solution to remove any mineral buildup. Place in a solution of one (1) gallon of water and eight (8) ounces of undiluted white vinegar. Allow the filter to soak for 20 minutes.
4. After soaking, rinse it several times with clean water. Place the PermaWick™ Filter in a location where it can drip dry while you clean the other parts of your humidifier.
5. Remove the water tank from the base and empty any water that is left in the tank. Soak the base in a mixture of one (1) gallon of water and eight (8) ounces of vinegar for 20 minutes.
6. After soaking, wipe the base with a soft cloth or sponge to remove any mineral build up. Rinse with clean water several times. If you are planning on storing the humidifier, be sure the base is completely dry.
7. Fill the water tank with one (1) gallon of water and eight ounces of undiluted white vinegar. Replace the tank cap and shake the tank vigorously until all interior surfaces of the tank have been exposed to the water/vinegar mixture.
8. Empty the tank of the water/vinegar mixture. Rinse it several times with clean water and then replace the tank cap. If you are planning on storing the humidifier, dry it inside and out, leaving the cap off to allow the tank to completely dry. Continue to clean the other parts of your humidifier.
9. Remove the water diffuser cap by squeezing the two tabs as shown in Figure 3. Rinse the cap in clean water to remove any debris. If the cap contains hard water residue, soak it in a mixture of one (1) quart of water and two (2) ounces of vinegar for 20 minutes. 41553-01 01/03/2008 6 © 2008 Hunter Fan Company
Rinse well and reinstall the water diffuser cap. Do not expose motor or other electrical components to water.
10. Wipe the surfaces of the main housing with a soft cloth.
11. Once all the parts are clean, reassemble the humidifier, and follow the USING YOURHUMIDIFIERto continue use. If you are storing the humidifier, make sure the parts are completely dry, reassemble, and store in a dry location.

Mine also cracked along the seam several years ago. I sealed the crack using two-part waterproof plastic epoxy (found at any hardware store.) Not really pretty to look at, but it hasn't leaked since!

http://homeappliance.manualsonline.com/manuals/mfg/vicks/v3100.html

This is the link to your manual.
Daily Maintenance
1. Turn switch to OFF position and unplug the cord from wall outlet.
2. Lift the Water Tank from Base. Carefully remove the Water Tray from the base being
careful not to damage the delicate Wicking Filter. Empty excess water from the Water Tray
without removing the Wicking Filter. Remove the Tank Cap and drain any water from the
Water Tank. Rinse the Water Tank with lukewarm water after each use. Wipe accessible
surfaces of the Water Tank and Water Tray clean with a soft, damp cloth.
3. Do not immerse the Base in water. For storage, wipe dry with a soft, clean cloth. Keep
water away from the Air Outlet.
4. Do not leave water in the Water Tank or Water Tray when unit is not in use as it may
result in the build up of mineral deposits and bacteria that can inhibit the output
efficiency of the humidifier. Please note that if water remains in the Water Tank for more
than a day or two, bacterial growth is possible.
5. Replace Water Tray with Wicking Filter. Then replace the Tank. Humidifier is now ready for
use.
Weekly Maintenance
Removing Scale
1. Remove the Water Tank and empty any remaining water from the Water Tank.
2. Turn switch to the ON position, either low or high speed, and operate Humidifier until the
Wicking Filter is thoroughly dry.
3. Turn switch to the OFF position and unplug the cord from wall outlet.
4. Remove Wicking Filter from the Water Tray by carefully lifting straight up taking care not to
tear filter.
5. Remove the Water Tray from the Base. Fill Water Tray with undiluted white vinegar. Let
stand for 20 minutes.
6. Dampen soft, clean cloth or sponge with undiluted white vinegar and wipe out Water Tray
to remove scale. Do not use soap, detergents or abrasive cleaners.
7. Rinse the Water Tray thoroughly in clean warm water or put in top shelf of dishwasher to
remove scale and vinegar before disinfecting the Water Tray.

Disinfecting the Water Tray and Tank
1. Fill tank with 1 teaspoon of household bleach in 1 gallon of water. Let stand twenty (20)
minutes, shaking vigorously every few minutes, drain and rinse with clean water until the
bleach smell is gone. Dry with a clean cloth or paper towel.
2. Wipe the Water Tray with a soft cloth dampened in the bleach and water solution. Rinse
the Water Tray thoroughly or place in dishwasher before proceeding.
3. Wipe all exterior surfaces of the Base with a soft, dry cloth. Do not immerse the Base in
water or use water to clean the base. An electric shock may result or the humidifier may
be damaged.

Hope this helps.
Good Luck.

sounds like new caps should solve it, but have you tried soaking the old caps in vinegar overnight? these guys are not the only ones, but they have the correct caps in stock at a pretty good price http://www.marbeck.com/humidifier_parts_bemis.html hope this helps :)

The part of the machine that draws water up from the bottom, as well as the bottom tray, need to be cleaned from time to time, or it cannot accept water and will indicate the tank is empty. After removing the tank, unlock the top from the bottom by moving the small lever in the area the tank sits, then pull the entire top section off of the bottom tray. Dump the old water out, then put a solution of vinegar and water in the accepting section of the tray. Replace the top and let that set for a few hours to remove buildup. You may need to use a silicone scraper or something if there is significant buildup. Pour out the vinegar solution and rinse all of those sections off with clean water. Replace the top, lock the bar, and return the tank. Your problem should be fixed.