Here is what Mr. Mendez recommended:
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"There are no shortcuts. If you want to play fast, first you must learn to play slow."
He demonstrated double and triple tonguing, and confessed it had taken a LONG time for him to learn them. He said his nickname as a child in his hometown in Mexico was "Mr. Tu-Ku-Tu," because everywhere he went, he was always verbally practicing the multiple tonguing syllables.