I have used this in conversation with 2 of my Welsh speaking friends recently, and drew blank expressions from both.
The wife of one friend, who teaches Welsh, says it’s not something used in this area. My friend who heard me say it today, is going to ask her cousin (whom I also practice with on occasions) who is a retired Welsh teacher and a linguist. I’m wondering where it would be used in conversation?
Interesting. I first heard it from someone who lived in the Rhymney Valley, so perhaps it’s just in pockets of south or south-west Wales. I’m fairly sure I remember it from the short lesson we had on Welsh to use at the rugby, so out of curiosity, I’ve hunted about and found that it still exists 
Common in parts of North Wales, also. 
I’ve heard it from teachers in the north of Powys. Haven’t heard it in my lessons in South Wales.
I made a “teisan rwtsh ratch” from a recipe I found on the facebook page Curo’r Corona’n Coginio.
Mae ’ rwtch ’ yn air cyfarwydd iawn yng Ngheredigion,
‘rubbish,’ ‘nonsense.’
'Ma fen siarad rwtch ‘achan’
