I used to have 2 sumps chained together (on th esame level), but I only used 1
pump although using 2 is a better idea (if one fails the other is still
pumping). I wanted all of my water to pass through the first sump then to th
esecond via a 2" pipe. A 2" pipe was not big enough, I had to divert some of
the water coming from the main tank into the second sump. if you aere using 2
300 gph pumps with one in each sump, you _might be OK with 1", but as Mark said
1.5 would be better.