I took on a big project yesterday. When I originally set up my two sumps, I used 3/4" tubing to connect them. The wall between them is 8" thick stone and that's the biggest hole I could drill with the tools I had. It's been a bit of a problem, though. There's enough resistance that I can't run the full flow of the return pump through it, so I have to put the return pump in the sump under the tank and use a second smaller pump to circulate between the two sumps. It also makes me extremely nervous because if that line were to get clogged up at all, the first sump could easily overflow. Soo... I went to home depot and rented a HUGE hammer drill and a 20" long 1.5" wide bit. It's really an incredible machine--it's like the BFG 9000 of drills. It cut through the stone wall like butter. I drilled several holes next to each other and knocked out the space between them, making a hole large enough for 1.5" pipe. Then I drained both sumps, stripped everything down, pulled them both out, scrubbed them, put them back, and replumbed with 1.5" spa flex. Now it easily handles the full flow of my return pump with very little resistance and plenty of room to spare. Yay!