Dean,
30 years ago I said that it wouldn’t break my heart to never do another one of them, but we still do 2 or 3 a month. Most are a breeze, some are a major pain. To understand what you’re dealing with, go to
https://fixradon.com/resources/library-and-links/ and scroll down to “Basement waterproofing”. You’ll see how Minnesota aftermarket drain tile is done- with a 2 inch layer of rock on the footing and the re-poured slab only 1-1/2 inches thick. Our homes with aftermarket drain tile almost always have block foundations, not poured.
The 2 inch 'air gap' between the slab and the footing is the major problem. Air is freely pulled from hollow cavities of the blocks through this gap. The gap between the slab and the wall is the lesser problem. We only seal them as a last resort and the improvement in sub slab communication is usually minimal.
With normal drain tile, we’ll cut a football size hole in the top of the drain tile at the suction point. With aftermarket drain tile, we’ll use a hole saw to make a tight fitting hole in the drain tile, cut the end of our suction pipe to the radius of the drain tile and then insert the suction pipe ½ inch into the drain tile for a tight fit. If the sump is where we want the suction, we’ll go through the floor next to the sump, turn 90 and enter the sump through the side wall through the proper sized hole saw hole. My theory is that we lose less vacuum through the air gaps with an “airtight” connection to the drain tile system.
95% of the time, one suction with a RP145 does the job. If not, we start doing communication testing. Avoid the temptation to just put on a bigger fan- you’ll exhaust a lot of house air, and could cause back-drafting.
We’ve found that unless we’re creating some vacuum in the drain tile, it usually doesn’t work.
Sometimes you’ll need more suction points on the drain tile. If your suction is tight to the drain tile, the end of the suction pipe is inches from the bottom of the drain tile. This creates turbulence and you lose a lot of air flow requiring more suction points.
Sometimes you’ll abandon the drain tile suction points and do suction away from the drain tile.
Sometimes you’ll do suction away from the drain tile with dampened suction points in the drain tile.
Sometimes you’ll wish you never took on the job.