Second, under Senate Rules, a senator may hold the floor for as long as he wants, barring a vote of cloture. Cloture stops debate, but under the rules you need a 60% affirmative vote (note 60%, not necessarily 60 votes if all Senators are not present). Debate may be temporarily stopped with a recess or another privledged motion.
another motion is called a "Quorum Call" (or Call of the House). All Senators are obliged to answer a quorum call by answering in person the roll. The President of the Senate may even send out the Sgt at Arms to enforce attendence. Here is a passage from Roberts ...
"Proceedings in a Call of the House. When the call is ordered the clerk calls the roll of members alphabetically, noting the absentees; he then calls over again the names of absentees, when excuses can be made; after this the doors are locked, no one being permitted to leave, and an order similar in form to the following is adopted: "Ordered, That the sergeant-at-arms take into custody, and bring to the bar of the House, such of its members as are absent without the leave of the House." A warrant signed by the presiding officer and attested by the clerk, with a list of absentees attached, is then given to the sergeant-at-arms, who immediately proceeds to arrest the absentees. When he appears with members under arrest, he proceeds to the chairman's desk (being announced by the doorkeeper in large bodies), followed by the arrested members, and makes his return. The chairman arraigns each member separately, and asks what excuse he has to offer for being absent from the sittings of the assembly without its leave. The member states his excuse, and a motion is made that he be discharged from custody and admitted to his seat either without payment of fees or after paying his fees. Until a member has paid the fees assessed against him he cannot vote or be recognized by the chair for any purpose.
In fact, not attending a quorum call would be very bad for the Dumbocraps, because if the Dumbocraps assembled do not make up more than 60% of the members present, a cloture vote can be immediately moved. In fact, at the quorum call, the doors can be locked to bar tardy members. If successful, the cloture vote would end debate and lead directly to a vote on the confirmation.