There are 3 passes between Glen Etive and Glencoe. None of the routes are very handy for the Clachaig.
These are:
1) Lairig Eilde - between Dalness and The Study at the head of Glencoe proper - from NN171514 to NN187563. Ive not done this route, so I dont know what its like, but it appears to be very straightforward on the map.
2) Lairig Gartain from NN171514 to NN213560. This has some quite steep places with some mild scrambling after about 1km and is then easily followed to the summit of the pass. The descent to Glencoe is a bit boggy in places but otherwise is pefectly straightforward and the path is joined by a descent route from Buachaille Etive More which makes it a bit boggier.
3) Minor road from NN171514 to 246550. Very easy walking on tarmac. (But you dont want to do this!)
To get to Clachaig from Dalness more directly, the options seem to be either a high level mountain route over Bidean nam Bian or a route joining Gleann Fhaollainn with Fiionn Ghleann. - Or a walk through Bealach Fhionnghail, which is the one I think I'd go for. NN131523 - contour NW at the North end of this route to avoid a problematic river crossing.