I have used a nappy bucket has a great seal followed some of the plans here and its been working great for the past 2 months! and a under water pump inside the bucket and making a hole for the power lead out of the bucket side
I was having problems with either the water would drain into the bucket faster than it would pump out or it would pump out mor from the bucket than it would suck out of the tank.
when it all came down to it all the problem was the tank intake pipe.
I had been getting very annoyed all day trying to work out what the problem was so i swaped the spray bar for the intake.
the water level started to drop and then it suddenly stoped going down and stayed at the same level with out raising or falling.
Taking a close look at the intake pipe (the spray bar) i saw the level of the water was just below the top of the last hole and sucking a little air into the pipe so i drilled a hole into the tank intake pipe (and put the spray bar back) and it work fine without a problem at all.
just one more thing because of the air going into the bucket i had to make a small hole in the lid of the bucket .
to prime the pump all i have to do is hold the pipe from the lid of the bucket while its sealed on the bucket and cover the small hole in the lid and gently push the pipe up and down and it runs great.
This has been a great project