I recently purchased a 2007 Keystone Hornet 28bhds. It was winterized, but now I need to empty out the tank to put in fresh water. Where's the drain?

Usually behind the bulkhead where the city water, tank flush, water filter and winterize valves are. Sometimes there is even an access panel inside the passthrough bay to get to it.

The water tank drain should have a shut off valve to prevent water leak. I wouldn't cap it, you should want to drain water tank on occasion.

There should be plugs underneath the camper to drain the water tanks. Remove them and let the water drain. There should also be a plug on the water heater, remove and let water drain. There is also a bypass valve on the water heater to divert water away from the heater, turn this to bypass. After the water has drained replace the plugs except the water heater plug. The heater plug can stay out. Fill fresh water tank with RV antifreeze, usually about 3 gallons or maybe a little more for larger RVs. Run pump opening faucets one by one till water is forced out and the antifreeze flows including toilet. When antifreeze is flowing out the faucets close faucets and shut off pump. When pump is shut off open faucets, the antifreeze may get slushy in very cold conditions but wont freeze and a little may drip out of the faucets. The water heater may still have a small amount of water in it but shouldn't be a problem if you leave the plug out. Make sure the blackwater and greywater tanks are empty, you can dump a little antifreeze down the drains and toilet to make sure the sink traps are free from water and the blackwater tank has antifreeze in it. Other than that just shut the propane tanks off and youre done. Try to leave a couple of windows cracked slightly to promote airflow and reduce condensation inside the camper

Keystone's have two water drains under the outside stairs unscrew those and most of the water will drain. once those have drained add your antifreeze to you fresh tank and run you pump. then make sure you add it to all drains. Do not for get to to unscrew you hot water drain. Very big socket.

Drain the supply tank (or run the pump until it sucks air) then pour a little RV potable antifreeze into the supply tank, open each faucet/outlet -- one at a time -- and run the pump until antifreeze appears at that faucet, close it and go to another one until all are running antifreeze - they color it to make this easy. All piping and pump and tank is now full of antifreeze and protected. In the spring put a little fresh water with a dose of chlorine bleach in the tank, run that through all outlets, fill tank with clean water and run that until you can't smell chlorine. System is clean and ready for use.

ok, been a while so lets ee if I can get this all down.

1 - Drain water from your holding tank and remove drain plug in hot water heater. Drain holding tanks ( Waste )
2- turn on bypass for hot water heater ( instruction if needed )
3 - Get yourself some winterizing fluid ( can't remember exact name ) from your local Dealer . 2 or 3 gallons should be good
4- Poor this fluid into your water rez tank. All of it
5 - now go around to EVERY tap in your trailer ( one at a time ) and turn on cold water until water runs pink ( or what ever colour fluid you bought ) Close faucet them do the same for hot water tap. Repeat this at every faucet. Even the ones outside if you have any.
6 Don't forget to flush toilet in water runs pink.
7. Ensure all gas vales have been turned off ( tank vales included )

If you did everything right you should be good to go.

Plz double this list to make sure I covered everything

Pull bottom plug out of hot water heater tank let all water drain. Then open all water tank drain valves and be sure your RV is tilted so it will drain towards the valve. Go in RV access water heater valves put it in bypass so no antifreeze can enter water heater tank. Pump RV antifreeze with hose provided into all water lines throughout RV by turning on your main water pump after you have stuck the bypass hose in a new and full antifreeze bottle, then flush toilet until red antifreeze comes out. Open all faucets one at a time until red antifreeze comes out. I use 3 gal but some only use one, the more the better it’s cheap at Walmart. Don’t forget to run outside shower until red antifreeze comes out also, very important or it will crack in the cold. Finally make sure black and grey tanks are empty and flushed at your last camp trip before winterizing. Pour antifreeze in toilet and all drains making sure first that black and grey tank shut off valves are pushed in and closed. Get a quality cover and store RV, it makes a huge difference on protecting roof and roofs lap sealant! All RV antifreeze is non toxic and you just drain it all at your first camp stop after winter! Note: don’t forget to put water heater ionizer drain plug back in wrapped with new white Teflon tape and take water heater valves out of bypass! Draw a diagram of regular mode and winter bypass mode so you don’t forget especially hot and cold water heater blender valve between the two MUST be shut off after you unwinterize
or you will cool your hot water unwanted and have no hot water to use! Happy Camping folks!

Should be right on or near the fresh water tank.

Should be at base of tank. Crawl under and look for small 1/2 hose pointing straight down. This should be the drain line. Follow it back to the tank. Valve will be there somewhere.