This is the foundation of a sub irrigated planter or SIP

I have used these outside and still have the pieces.
I used a few 30 gallon totes with the bottom having drain tile 4 inch in the bottom. You have a hallow stalk down to about 3 inches from the bottom and a drain hole at 4 inches. The tote is filled with clay pellets to the top of the drain tiles and then soil.

The system works on the principle of sealed water in a tube that when the water level drops below 3 inches the bottle you mount on the top of the stalk glugs back up to 3 inches.
The drain at 4 inches is to relieve rain water that would drown the sip.
Search sip and I do know you are not looking for a sip but the principle should work for you.
Google building a sip

Ive done this with mine , i know the last couple of grows i was drying out at the bottom of the pot ...not anymore, Ive laid the pipe along the bottom and drill loads of holes in it...i was thinking 1 watering out of 3 i will stick half a litre down there and let it soak up. i might even use it more at the start to try and get those roots down there