It basically depends on your growing medium, watering schedule, plants your growing, size of the containers, temperature, so it really depends on what you are going for. If you want a small amount (reserve) left in each bucket, you can use the "U" shaped tube. If you are looking for more/better drainage, the straight tube would be the way to go. You can also set the overflow level to any height you wanted to adjust how much is left at the bottom in-between cycles.

how do keep the reserve nutrient solution fresh in the bottom of the dutch bucket system?
Does the inverted U create enough suction to remove the "older" solution?

thank you,

I have been growing in bato buckets for years and always used the U shaped siphon tubes. I know that when I shut off the nutrient feed I am left with about 1 1/2" to 2" of solution in the bottom of the bucket. My flow rates are sufficient that every time I feed, enough solution enters the bucket to displace the older solution on the bottom.

One advantage to having the solution on the bottom is if I am away for a day or two and for some reason all or even one bucket is not refreshed with new nutrient, there is a reserve on the bottom so the plant can draw from it. This has saved me more than once.

For these reasons I would vote to add the U tube so you are assured to maintain the liquid on the bottom and make sure your flow rate feeds at least the volume you retain daily to keep the reserve fresh.