So I came up with this idea and have used it on two Dry Start Method (DSM) scapes thus far. I feel that it helped with my DSM scapes by keeping moisture in the substrate at an optimum level as well as some other bonuses that I will share.
Those with short attention spans - it's a drain that keeps the substrate from accumulating too much moisture.
It's entire purpose is to keep the substrate base moist and prevent it from being overly saturated. It does this by action of siphon and capillary. The added bonus I have also found, is the ability to remove ammonia leach and observe by way of testing the water removed, is that the substrate base becomes biological active with the presence of nitrates.
I have not seen or read any others doing this, so for the purpose of naming it for discussion, I have dubbed it the "Bala Drain". (Bala de Plata is a handle I have had for many years and use on "other" forums)
It is a very simple assembly of a couple parts which many will have on hand and use in a different manner (like drip acclimation). It simply consists of airline tubing with a ceramic/stone type airstone on one end and a airline flow adjuster at the other. I have found that the composite/cheap "plasticy" air diffusers do not work well for this application. You can add a airline suction cup to help secure the airstone in the substrate if it's felt necessary.
When starting your substrate base, choose a location that you can bury the airstone connected to airline tubing (leave the tubing long, you can trim it later). You can put in a back location where it will be very deep or in a foreground area where it is shallow. Only thing that is important in this step is too have it be fully beneath the substrate on the bottom of the aquarium with at least 1/4" to 1/2" of substrate cover. This is necessary so the airstone can absorb moisture evenly and help with the capillary action of drawing water in. If you put it in a shallow foreground area, you could easily recover the airstone without too much disruption to your scape. But if you placed it deeper or choose that you do not want to disturb the substrate or carpeted growth, you can simply cut the airline tube beneath the substrate and no one would be the wiser.
Now that the airstone is buried, just drape the airline outside the aquarium. For the system to work well, the outlet needs to be below the aquarium. If the aquarium is on a raised stand, the outlet should go to a container on the floor.
Proceed with wetting/moistening your substrate in whatever manner you choose, (thanks to the drain you installed) do not worry if you over water the scape a little too much. In fact this makes it easier to get the drain working.
To start the drain, you want to VERY slowly draw water into the airline tubing. You can use a plunger of a syringe or any other way you are comfortable. You want to get the water up the airline tubing and then past the point of the bottom of the aquarium. Once water in the tubing is passed the bottom of your aquarium, it should continue to flow on its own gently (like a tiny siphon). Just understand that the goal is not to get a lot of water out quickly. Think of it in terms of BPS (bubble per second) as used with co2. But instead it is SPD (second per drop) which the goal should be anywhere from 2 seconds a drop to 10 seconds a drop. Also, you want to prevent air from getting into the airline, this will break the siphon/capillary draw. However if a small amount of air gets in it should not break the draw. But if it is continually drawing air in, you are either drawing too fast on the outlet, the airstone is not sufficiently covered, or there is not enough moisture to draw out of the soil and a drain is not necessary yet.
So with your drain primed and dropping very slowly, you are no able to drain off excess water over the course of a couple hours or a couple days. All depends on the size of your scape and the amount of water in the substrate. On my mini m I only drained off about 2 cups every other day. On my 90p I drain off about a half gallon every 3-4 days. Now what this also means is that I am misting and spraying every other day or so in amount close to equal what I'm draining off.
Which means your doing water changes on your DSM.. Mind blown yet?
Think thats enough for now. I can answer questions or explain something better in responses or edit the OP later.
Bala Drain.. It's for DSM's