You can buy a rubber tipped air nozzle from Harbor Freight for a few dollars and a cheapo regulator for about the same price that regulates down to under 10 psi.
If you also get a press fit to 1/8" pipe thread hose connection from your local Parker distributor and a couple feet of nylon hose, you can make a tool to test the drains. You screw the 1/8" fitting in to where the interchangeable nozzles go. Use very low PSI when you do the job. You can also use the tool to blow air up into the two drains next to the transmission that drain the AC condensation reservoir that has caused the wet carpet in my 2001 several times.

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2001 x5 3.0 (sold with broken motor), 1990 e30 M3, 1991 318is, 2002 325i, 2008 335i Dinan stage 3 6 speed,