The threads are stripped on my Hayward sand filter drain plug.

I've had the same problem every year since I bought this house 10 years ago with my Hayward filter drain and finally MacGyvered a great solution. Went to Home Depot and bought a 1" PVC shutoff valve. The Hayward drain has an outside 1 1/4" thread. The part I got was an 'Aqua-Dynamic' 1" PVC Schedule 40(I can't find a picture of it on the internet). It is a white PVC valve with an inside thread that mates with the Hayward and a red shutoff winged knob. You need to hacksaw the red wings off the knob in order to be able to screw it onto the drain because the filter's base gets in the way. Leave the valve in the open position(especially if water is still draining with filter off) and put PVC cement on the outside of the drain thhreads and a bit on the inside of the valve and screw it on. When the glue dries(5 minutes), you now have a drain that you can open and close every year with ease(you need a pair of pliers because the wings are off the turn knob but it works great!)

Purchase PVC female connector/coupler with1" ID threads on both ends. Purchase 1" male PVCplug. Apply RTV silicone to stripped drain threads...also apply silicone to the threads on one side of the female connector/coupler. Screw connector onto drain. Wait 24 hrs for silicone to cure. Screw in plug into the other side of the connector. Fixed for about $2.50. Parts purchased at Lowes.

Thats about all you can do without replacing the filter housing.. Good luck

Just wanted to say this thread helped me with the same problem. The male threads on my sand filter drain outlet pipe were stripped and it was also warped so my drain cap was not sealing. I ended up using pvc primer + grey cement to attach a 1" threaded 45 degree elbow to the drain. Apply the cement liberally and also apply a bit to the outside once the 45 is threaded on. I also added a layer of GE white silicone to the outside (use a popsicle stick to seal around the whole pipe where the caulking gun would not reach) in case the cement did not totally seal. Then I connected a 1" fully threaded nipple and 1" threaded ball valve with teflon tape to the 45. I purchased the ball valve from Home Depot and other fittings from McMaster Carr. So far no leaks.

Or on inside of plug hole to filter fit a small closing plug tighten it up and put cap over it

I ended up trying this before I had to buy a while new filter cannister etc for about 500 bucks. I epoxied the existing cap onto the stripped threads on the outlet. After it set up, I drilled a 1/2" hole in the center of the affixed cap. Bought a tapered rubber stopper to jam in the hole. Worked fine last summer. In fall I pulled out the stopper with pliers, and the water drained out. Will see if it works again. cost: about a buck. Got another year from the filter.

Here is another solution but this option will allow you to open and drain at any point with ease and then turn it back off with ease as well. Purchase the following: PVC female connector/coupler with1" ID threads on both ends $.90 cents. 1" male threaded to 1/2" Female threaded PVC bushing $.70 cents. Orbit 1/2" x 12" flexible riser (Blue) threaded on both ends $2.87. 1/2" PVC Ball value threaded $2.65. Apply teflon tape to all threads and assemble as picture demonstrates.