a 1/4" air line is not sufficient for that sized pump. It is designed to handle multiple 1/4" lines. You could use a section of garden hose for an air line or go to lowes and buy some 1/2" clear tubing. The 1/4" line put too much back pressure on the pump and may have blown the diaphram in there. The Dolphin AV-50 can sit in the rain....mine have for several years now with no ill effects. But yours is an AV-50? Not sure if it has a weather proof housing or not. How much do you want for the dolphin? I many be interested in it. Or you can try craig's list.

The verticle height is about 8 ft, so removing or disabling the check-valve is probably not going to work. pjb999, if your in my basement, the tubing runs parallel in between 2 joists. In a most houses here, the tubing would penetrate the plywood siding to the exterior (just like most outdoor faucets are installed. However, my kitchen sink area is like a bay window, where the floor extends past the foundation, about 2 feet. Because of this, once the tubing is past the foundation wall, it is routing down so it penetrates the plywood straight down. From the outside, I can get on my back right under the bay window area and look straight up and see the tubing. Maybe I can try making a hole about a 1/2" below the point the tubing meets the outside plywood, and see if that helps with the draining. I was thinking of a T, but I'm not sure if I understand how you are proposing. From the sound of it, I'd end up with 2 tubes holding water. Unless you are suggesting I have the tubing from the second T drain back into the pump basin?

Yeah, and it's not even 60 gallons. You're not filling them to the top. I average around 3 gallons of actual solution per bucket but I use net pot lids that are much deeper than dropping a 2 or 3 inch net cup into a flat lid so my water level is lower which as you found out makes for less water pressure pushing back on the air stones. Even a gallon can make a difference. http://www.amazon.com/Hydrofarm-AAPA45L-20-Watt-Commercial-Outlets/dp/B002JPRNOU That is the exact pump I use but for half the amount of buckets. You could use that but would have to split the lines off the manifold since it's only a six. 700gph vs the 48gph you're using. Massive upgrade. Then when your plants start developing nice root structures drop the water level down for less back pressure. You could even just keep the air stones higher in the bucket like you stated earlier when you're water levels are high but I don't think you'd have to do that with that pump even powering 12 buckets but you'll always have that option. Small price to pay for healthy plants. I just harvested several pints of cherry tomatoes off one of my red robin plants. When you get to do that and not go buy them at the store it makes it easier to justify costs. IMHO.

I don't have equipment to measure the pressure differences but I have done some qualitative tests to evaluate the velocity of air that comes through a known opening (small window) for H/M/L blower settings as well as the velocity of air exiting the blower exhaust. What I found is that the pressure difference between the kitchen/dinette/family room space is greatest on the LOW blower setting and less on HIGH and MED settings even though the volume of air exiting the house from the exhaust is H/M/L as you would expect. I attribute this to the lack of MUA on the LOW setting due to the closed MUA damper. The hood flow I am perfectly satisfied with although it bothers me that the low setting is lower than designed because of the lack of MUA. I believe replacing the airflow MUA switch with a simple current sensing switch will be a good solution. We live in the PNW with a fairly mild climate with low temperatures seldom below freezing and never below 0 degree F and our furnace does not seem to have any trouble keeping up with the colder MUA inflow so far (although we have not had many cold days yet). opaone: Our MUA damper is a Broan MD10TU with a motorized damper triggered by a remote flow sensor switch. Thanks for the input on interlocking the MUA with the blower - I had thought that would be a good idea for MUA performance but not considered the static buildup aspect. The 6" MUA damper originally installed with the furnace is interlocked with the blower so I guess I better research how that works. And thanks for the kitchen compliment.