Here's how I modded the RC Tank for the Eheim pump...
thought you guys may wanna see this...
Plumber's goop works like a charm here - as always-

2cm wide hole in da tank!
additionally you can use some conformal coating here:
I've been testing it for about a week now, no leaks whatsoever...
BTW I still think procooling style RC Tank mod is the best though
Bruce