Water fill issues on 84FCSB

[hippieforever3]

I'm down to minor problems but I still have an "annoyance" that really needs to
be taken care of.

I repaired a crack in my watertank and in the process sealed a small hole a few
inches up over the small depression under the two drawers under the driver side
closet.

I have an overflow tube (similar to a pool cleaning hose - ribbed) that has a
"U" bend in it and exits though the floor near the driver side rear closet.

My "annoyance" is that with the small hole sealed and the overflow tube tight
enough to prevent a lot of leakage while filling, I have twice ended up creating
a siphon which starts to drain the tank after I turn the water off. Normally I
would just wait for the siphon to break BUT on both occasions I've watched this
with the tank exposed, the siphon is strong enough to make me fear the tank
might be damaged by the stress.

Can someone definitively tell me what the stock configuration was?
Was there some sort of relief breather hole or not?
Was the overflow tube sealed well enough to create a strong siphon?

Other than very carefully monitoring the water level while filling, has anyone
found a solution?
Do other people even have the same problem?

Regards,
GPSGary
84FCSB