'98 LSS CEL, purge canister issue

My '98 Olds LSS (Eighty Eight, 3.8L, N/A) has a constant check engine light. The previous owner's (halfassed) mechanic said it had to do with the fuel/purge canister system. A new gas cap was tried, no help.
So, having not yet gotten my hands on a code reader, I checked the vent system. All of the lines from the tank to the throttle body are free and clear, and both solenoids work when +12v is applied (the one on the canister closes, the one near the TB opens).
However, with the gas cap off I can not blow any air through the vent line from under the car. I would've thought that I'd be able to pump air right through it. Is there a check valve or another solenoid ontop of the tank that I should know about? The entire fuel sending unit was replaced by said mechanic a while back, I'm wondering if he buggered something up, up there. It has been known to hiss when the gas cap is removed, so hopefully it's something obvious up there. Comments? Suggestions?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Check the filter on the evap purge valve, they get plugged with dirt and dust. The code set would be P0446. Quite common for drivers on gravel roads.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Checked when I checked both solenoids for proper operation. I could blow through it with no obstruction (until I applied 12v of course).
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.