When two letters both have dhammah appear one after each other - do the lips remain in the outwards dhammah position after executing the first dhammah letter?

Question
Asalamualaikum,
When two letters both have dhammah appear one after each other - do the lips remain in the outwards dhammah position after executing the first dhammah letter to then enter the next dhammah letter?
Or does the lips go back to neutral position after saying the first dhammah letter and then again enters the outwards dhamma position for the second letter?
Answer
Wa alaikum assalaam wa rahmatullahi wa barakatuh
When two juxtaposed letters have dhammahs and there is no sukoon between them, we put our lips in the dhammah for both without going back to neutral.  The only time we return our lips to neutral is when there is a sukoon in between two dhammahs (or any other vowel). 
To pull back and go out when both have dhammah would require exaggeration and effort which is not needed to convey the correct vowels.
Baarak Allahu feekum.