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I have a limited knowledge of how a sewer system works, so I come to the experts to find answers for two plumbing questions. 1. We have copper pipes. What is the cause of a white/yellow crystalline corrosion at nearly every solder joint? Is it serious? 2. Why is it that nearly every time we flush a toilet, there is a blub of air that comes up through the bowl and the toilet won’t flush well? (I assume a venting problem is the answer). Background: Our house is two years old. It passed all “inspections” per the city inspection office. We are on septic, which drains very well. We have copper supply lines and PVC drain lines. For toilets, in this day of 1.6 gal flush, I managed to get 3.5 gal Gerber elongated bowls, we have 4 toilets. One of the 4 toilets ties in to the soil stack at the very end of the soil line and has its own venting through a 2″ pipe. The other three toilets tie into the soil line very close to each other, in the line, and their 2″ vents eventually all interconnect at a single 2″ pipe through the roof. Two of the toilets empty into the soil line near an area that “flows up hill” about 2-2.5″ (we all know it won’t flow up hill). The roof pitch is 12/12 and all the vents are near the bottom section of the roof. I notice that the venting problem is more pronounced when there is a big change in air temperature (usually from hot to cold).