I am going down the plated column path and if you look at 5Star's "Jumping on the Bandwagon" post you will see he has done a lot of the hard work for me :D
I have cut the 4" pipe into sections and have used heavy duty T-Bolt clamps to pull it as true and round as I can get. I plan on soldering each plate into the sections that way it should have watertight seal around it not matter if the pipe is still a little out. Then wrap some teflon tape around the join and clamp each section together with the stainless steel T-Bolt Clamps. In the practice run I bolt all four sections together and lying it between 2 saw tables it could just about hold me weight pressing in the middle of it, so there is not way it will fall over, and hopefully the tape and the solid surface of the clamp and the pressure of it will make a leak proof seal.
I just need a bit of advice before I solder up the plate, I have drilled all the perf holes and hole for the down dropper, Planning on using 19mm down pipes into a 25mm cups ( is that size alright?) I just want to check do I leave about 20mm above the plate for the dropper and about 30-40mm for the cups ???
Also do I drill a couple od small holes in the side of the cup at the bottom to allow it to drain out at the end of the run??
Jamjar