WOW NICE!
Lol ... stoned.. i might be able to help you ... I did this mysefl and it looks bad ass!!!
Check out my sig for first dwc grow.
anyways go into pvc department look for ball valve drain, I think you need 1/2 inch... IF you decide that you want to hook directly a hose up to it so that you can take another garden hose hooked up to your kitchen or whatever sink inside the house with a adapter and wash out all the build up on bottom and on sides! and you will not have to constantly dump out a bucket cause its already doing it!
My sig has decent pics of this and I think it be great...For safety issues, i went to petsmart to buy aquarium safe silicone.. I did not want any toxic problems and it was plant and fish safe... Cant complain..
I bought a ball bearing darin valve with a connector piece. I took the connector piece and used a sharpie to trace the size of the hole. I used my dremel tool to cut the hole. There was a snug fit. I applied liberal amounts of silcone both inside and outside container. I mean lots! dont be afraid to use 60 percent of the tube. I did this because I had a slight leak issue and i was not applying that much.
There might be better ways to seal the tub, but I found with the silicone and care used when draining i have no issues.I just make sure that the hose isnt pulling the drain valve completly down... if needed i give support. I have to because my tub is above ground. Anyways I have lots of pics to provide in my dwc link under my sig.
I be more then happy to go more in depth..
BTW I actually forgot... I made 2 DWC.... just like mine which is use. I could always sell you mine.... just a thought... I took lots of time in building it and cutting 3 net holes to get perfect fit. As well the covering for the tub, to prevent light coming thru.