Cleaning cast ion griddle- what I do is, after preparing the dosas, I dip a paper towel in a bit of oil & apply it on to the tawa when it is still hot(imme after making the dosas) & just rub off any dosa pieces sticking to the tawa.... The next time I use the tawa, I just hold the tawa under running water for a few secs so that the excess oil applied & any dust that has accumulates goes off...No scrubbing or soap used...
Also, I have used the same tawa for making chapathis a few times... what I did was I applied little oil whenever the tawa became too dry & once I finished making all chapathis, I applied a good coating of oil when the tawa was still hot... The next time I made dosas, I didn't have any problem of dosa sticking to the tawa... But I am not sure if it can be used safely on a regular basis...