Multi reel tank leakage

[esearing]

I am using a 5 reel Nikkor stainless tank with rubber daylight funnel/lid to process my 5x12 negatives. Requires about 1800 mls of developer. My issue is that it leaks 30-50mls during a 13 minute cycle. I initially agitate/invert for 2 minutes then 2 or 3 more 20 second inversions during the remaining time. The top edge of the film is still covered while resting unless the negative floats up.

Is there anyway to seal these up a bit more to reduce leakage?

 

[BAC1967]

I always seal it with electrical tape and hold the fill cap down with one hand while I’m agitating.

 

[esearing]

I tried electrical tape between the lid and outer part of tank but may try actually taping the lid to the tank after it is on the tank. As for the small top funnel lid I may try a flat rubber gasket or bottle cap liner in the lid next so it seals the opening better.