thanks.
1 a non return valve is unlikely as it drains in the same direction as the pumped flow.
2 the cap has a breather to prevent a vacuum forming,so
sealing it would create problems.
but thanks for replies.
colin m
colin m, April 2011
Don't fill it to the top, make sure the top is on securly and seals the neck, park facing downhill?
arizona kid, April 2011
There is a non return valve in the pipe,it is probably stuck.
