if your thinking a 10-20L tank because it will be easier then think again. anything smaller than 30L and you have to be very very carefull with water chemistry, temperature, oxygen, and stocking.
most people use plumbing pipes from hardware store. or I suppose you could use the pipes from your canister filters if you want them to be flexible.
to use one sump for multiple tanks two pumps would be essential. that way you can turn them off seperately and adjust the flow to suit the different tanks needs. people also put their heater in the sump too to tidy up the tank. it would need to be a big one though (even if you left the heaters in the tank a bigger one might be needed anyway as you will have more water to heat)
anyway someone else must have more experience than me
ive never used a canister filter but have always liked the idea of sumps. my next tank..... will definitly have a sump. the tank needs to be built for/modified for them though, so if you already have fish in them it might get a bit tricky. I love the idea that they are so customisable and they increase the water volume of your tank. glass is expensive though. wonder if anyone has tried acrylic?
did a swap for my geophagus today. my tank now seems super empty as they are hiding atm. boy was the geo hard to catch. i had to remove 1/2 my plants and wood to deprive him of hidey holes!
moved my heater and it seems to have fixed the problem. was trying it in the corner by the filter but these cold nights are too much for it there. in the middle now and its 26 degrees.
lol your right I was thinking mm. was still waking up when i wrote that! anyway my 90Lx30Wx45D tank has bracing across the middle so I waould say that a 180cm long tank would definitly need it!