Re: Double Tonguing
Double tounguing, IMHO, is a procedure that works best for brass and flute, rather than reed instruments. With those, tonguing merely stops the airstream, so t-d-t-d-t-d works, and triple tonguing t-d-k-t-d-k works as well.
With a reed instrument, like saxophone and clarinet, tonguing generally stops the vibration of the reed, so only the t works exactly right. The d and the k might stop the air, and therefore the sound, but to me it sounds fuzzy.
Although, if you're playing fast enough so that double-tonguing or triple-tonguing is required, it will probably be too fast to notice the less than pristine tongue.
My advice is to get your tongue to work as fast as possible without double-tonguing, but to practice the double-tonguing slowly to get the best sound, and gradually speed it up to what you require.