Shower won’t drain

[bobputt]

The shower inMy flagstaff 25FKWS travel trailer sometimes won’t drain, even when the gray tank is empty. Water will also back up in the bathroom sink. I opened the vent under the sink and the sink drained, but not the shower. The shower finally drained when I emptied the black water tank. Any suggestions how to resolve this issue?

[upflying]

Sounds like your gray water tank isnt venting. Did the shower drain before? Is the vent on the roof blocked by ice?

[bobputt]

Thanks for all the replies. Look like my vanity sink vent was the culprit. After a short ride today I set up and so far everything is working. I must have been mistaken as I am now sure the shower is draining in the gray tank as it should be.