AN INSTRUCTOR PLT RPTS THAT HE WAS UNABLE TO MAINTAIN AN FAR MSA AND VISIBILITY AND CLOUD CLRNCS WHILE PROCEEDING THROUGH CLASS G AIRSPACE TO THE FINAL DEST. AN INST APCH INTO A CLASS D ARPT WAS USED TO GET DOWN BELOW THE WX; AND THEN IFR WAS REPLACED WITH A SVFR TO DEPART THE AIRSPACE. THE INSTRUCTOR CONTINUED TO THE DEST AT LESS THAN 1000 FT AGL OVER A CONGESTED AREA.

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I WAS ON AN IFR FLT FROM BLI TO S50. WX IN THE SEATTLE AREA WAS BELOW THE 2000 FT MVA; SO I OPTED TO FLY TO MY ALTERNATE; BFI. MY INTENTIONS WERE TO SHOOT THE ILS RWY 13R AT BFI TO GET BELOW THE CEILING; AND THEN PROCEED VFR S DOWN THE VALLEY TO S50. AT THAT TIME; BFI WAS RPTING 1300 FT OVCST; VISIBILITY 2 MI IN RAIN AND FOG. I RECEIVED AN SVFR S. I WAS TOLD TO MAINTAIN SVFR WX MINIMUMS AND STAY BELOW 1000 FT; AND TO RPT WHEN CLR OF BOEING CLASS D. APPROX 3 MI S OF BOEING; I SWITCHED TO SEA APCH FOR FLT FOLLOWING. I WAS MAINTAINING 550-600 FT TO REMAIN CLR OF CLOUDS. I RPTED I WAS CLR OF BOEING CLASS D AND WAS TOLD BY SEA APCH TO MAINTAIN VFR. I COULD NOT MAINTAIN 1000 FT ABOVE THE CONGESTED AREA I WAS OVER AND ALSO MAINTAIN VFR. I CHOSE TO REMAIN VFR IN UNCTLED AIRSPACE BELOW 700 FT AGL. THE FLT ENDED WHEN I SAW S50 AND LANDED. THE REGS ARE CONFLICTING. AREAS THAT ARE CONSIDERED CONGESTED ARE NOT SPECIFICALLY CHARTED. ALSO; FOR ME TO MAINTAIN 1000 FT AGL WOULD HAVE BEEN ENTERING IMC IN CTLED AIRSPACE WITHOUT A CLRNC. I FLEW DOWN THE VALLEY OVER HWY 167; SO THAT IN THE EVENT OF AN EMER; I HAD SOMEWHERE TO GO.