sounds like some kind of clog, maybe sediment or something similar... this is especially possible if you ever let the reservoir go completely dry. There are mineral deposits on the inside of the reservoir that can flake off if it stays dry for too long. These can clog the outlet line going to the washer pump.
"No matter where you go, there you are..." Buckaroo Banzai
2012 F30 335i | Black Sapphire Metallic | Black Dakota Leather w/ Red Accents | Bone Stock | 20" BMW Double Spoke 361 | Continental ExtremeContact DWS-06
1999 Alpine White 323i Convertible (gone but not forgotten)