I think my dad used electrical conduit, but not sure. Galvanized water pipe would be too heavy, conduit too flimsy.
I would think of using PVC.
Started to transplant the St. Anne lettuce and thought that was ridiculous, trying to transplant bunches of small lettuce plants is nuts. Was going to put them in a three foot long planter, so prepared the potting soil in the planted by sticking some Jobe spikes in it to jack up the potting soil as it has been there since last year, plus put some new soil in, and depressed the center all the way down the planter and put new St. Anne seed in there, covered them up and watered it and it's done. That's the first time I have dumped seedlings but my lower back said do it, so I did.
I am glad all those plants are in permanent containers. However, I've got some Lantana flowers in small pots they came in from Lowes, and I need to transplant those into larger containers. I probably have five of those at least, don't remember how many I bought that day. So, I guess I am NOT through transplanting, plus two more tobacco need transplanting. Crap, I will never get through with that.