Access hole in top of fresh water tank

[K/C and Pups]

Has anyone ever cut an access hole in the top of their fresh water tank. I have a severely clogged drain valve in the bottom of the tank, and I know I could unplug it if I could get access from above. All the tank fittings are located on one end of tank and I would like to cut a hole large enough to deal with all fittings in the future. Tank is non-pressurized. Tank is half full, and no idea how long water has been sitting. I read one post about algae growing in drain valve. I began to drain the tank and after turning plastic ball valve, which was hard to rotate, it was apparent it was blocked. It rotates 360, and I tried it in both directions in case they make a valve with only one entrance hole. All efforts from below, including high air pressure, resulted in a slow drip, to a small stream and back to a slow drip, to a complete stop. I added the chlorine sanitizer mix for my 65 gal tank according to another post, but so far it has not helped. Tried the fresh water pump to drain the system into the grey water tank, and quickly discovered the pitfalls of polybutylene tubing. Leak under the sink. Pex system in the works. I know chlorine eats at the poly connections over time. The access hole would allow my to get rid of the small 1/2" dia. plastic ball valve to a larger more efficient drain system if necessary. I could probably install a valve on the discharge side of the fresh water pump to aid in system drainage without filling water lines. Cutting the hole and building an access door out of aluminum or stainless would help the current problem, I think.

[Rickf1985]

You could do it and replace the hole with a boat bulkhead fitting but if the stuff in the tank is that bad you really should think about replacing the tank. Would you ever want to drink water out of that tank? I doubt you would ever be able to get the tank clean enough because the stuff is going to be growing everywhere in the tank including on the top side of the tank which will be hard to get to short of filling it 3/4 full of highly chlorinated water and driving around for a couple of hours to keep it sloshing. That will cost you as much as a replacement tank.

[K/C and Pups]

Rick, the water looks clean. I see no growth of algae or any discoloration,. That was suggested on a previous post as one reason my drain valve would not wok. I managed to drip out 2-1/2 gallons overnight. I plan on working on a leak today, and will attempt to fashion some sort of needle fitting for my compressor.
Thanks, I plan on ending up with some sort of way to dump the fresh water faster than a small 1/2" tube restricted by a valve reducing the size of flow.

[Rickf1985]

This is what I was thinking of for filling the hole you would make in the tank.

http://www.westmarine.com/buy/west-marine--screw-in-deck-plate-6-non-skid-white--11743101?cm_mmc=DC-_-Annual-Catalog-_-2015-_-Null

Can you access the valve you are having problems with to remove it? Or possibly force water backwards through it to open it up and then it might drain and you can remove the valve from the tank.

[Froggy1936]

My Son in Law purchased a 1977 Itasca from a Police Impoundment THey confiscated it from the drug runners when they arrested them . I Found the freshbwater tank had a 8 In Diameter hole in the top where they carried their drugs . So be careful of making a suspected drug mule R/V ! I just welded a patch on the tank had no leaks    Frank

[Rickf1985]

They would have to have a search warrant to go that far or a "permission to search" from you. Personally I would have no problem giving them the permission since they are going to get the warrant anyway if they suspect there is something worth searching for. They must have good reason to want to search your rig but even then,  there is nothing in the tank but water right? An RV is a rolling drug mule as it is if you think about it, all kinds of places to hide drugs and the cops are not going to be looking for the obvious ones. Cops are not bad people and they are not going to tear your camper apart unless you give them good reason to.

[K/C and Pups]

Rick, Thanks
You jogged my boating memory. A 6" from Jamestown is on the way.
when I blew compressed air thru the drain pipe from below, the wife said she could see bubbles in the water above the valve so I am making headway.

Frank, Good heads up. I have a friend in So. Cal. with the Border Patrol, so maybe he will save me.